Transcript Rheology of liquid media influences bacterial physiology Maja Borić

RHEOLOGY OF LIQUID MEDIA
INFLUENCES BACTERIAL
PHYSIOLOGY
Maja Borić, Tjaša Danevčič, David Stopar
University of Ljubljana, Biotechnical Faculty
IMPORTANCE OF RHEOLOGY IN
BIOTECHNOLOGICAL PROCESSES
Rheology studies the flow of liquids or soft matter
 Water treatment plants, bioreactors
 Influences pumping, hydrodynamics, mass
transfer rates and sludge-water separation
 Changes molecular diffusion as well as
movement of microorganisms
 Can a change in liquid medium rheology
cause a change in bacterial physiology?

CHANGING MEDIUM RHEOLOGY IN THE
LAB

Ideal polymer:
increases viscosity
 changes Newtonian liquid to non-Newtonian
 can not be degraded by bacteria and used as a
nutrient
 does not affect other physico-chemical factors (pH,
water activity, DOC)

Hydroxyethyl cellulose (HEC)
 Viscosity range: 0.8 mPas – 26.5 mPas
 Model organisms:

Bacillus subtilis
 Escherichia coli
 Vibrio harveyi

PHYSIOLOGY OF BACILLUS SUBTILIS
0,8
1E-10
-1
0,6
-1
growth rate (h )
-1
respiration activity (mL CO 2 h cell )
0,7
0,5
0,4
0,3
0,2
1E-11
0,1
0
5
10
15
20
25
30
0
viscosity (mPas)
-1
15
20

3,5
3,0

2,5
PFK (phosphofructokinase) – glycolysis
2,0

GPD (glucose-6-P-dehydrogenase) – pentose
phosphate pathway
0,5

0,0
0
5
10
15
viscosity (mPas)
20
25
Respiration activity is the same at all
viscosities
PFK
GPD
PK
4,0
specific enzyme activity (U mg protein )
10
viscosity (mPas)
Growth rate increases but then returns to the previous
level

5
25
30
PK (piruvate kinase) – flow to the citric acid
cycle
30
PHYSIOLOGY OF ESCHERICHIA COLI
1,1
-1
respiration activity (mL CO 2 h cell )
1,0
-1
-1
growth rate (h )
0,9
0,8
0,7
0,6
0,5
0,4
0,3
1E-12
0
5
10
15
20
25
30
0
viscosity (mPas)

-1
5
10
15
20
25
viscosity (mPas)
At the highest tested viscosity the growth rate and respiration activity decreased significantly
PFK
GPD
PK
6
specific enzyme activity (U mg protein )
1E-11
5
4
3

PFK (phosphofructokinase) – glycolysis
2
1

0,08
GPD (glucose-6-P-dehydrogenase) – pentose
phosphate pathway
0,06
0,04

0,02
0,00
0
5
10
15
viscosity (mPas)
20
25
30
PK (piruvate kinase) – flow to the citric acid
cycle
30
PHYSIOLOGY OF VIBRIO HARVEYI
1,0
-1
respiration activity (mL CO 2 h cell )
0,9
-1
-1
growth rate (h )
0,8
0,7
0,6
0,5
0,4
0,3
1E-12
0,2
0
5
10
15
20
25
30
0
viscosity (mPas)
5
10
15
20
viscosity (mPas)
V. harveyi increased its respiration activity in order to maintain an unchanged growth rate.
Despite this, the growth rate decreased at the highest tested viscosity.

PFK
GPD
PK
3,0
-1
specific enzyme activity (U mg protein )
1E-11
2,5

PFK (phosphofructokinase) – glycolysis
2,0

GPD (glucose-6-P-dehydrogenase) – pentose
phosphate pathway
0,5

0,0
0
5
10
15
viscosity (mPas)
20
25
30
PK (piruvate kinase) – flow to the citric acid
cycle
25
30
GROWTH EFFICIENCY
efficiency
2,0
A
1,5
1,0

V. harveyi (A)

E. coli (B)

B. subtilis (C)
0,5
0,0
0
efficiency
4
5
10
15
20
25
30
B
3
2
1
0
0
efficiency
4
5
10
15
20
25
30
C
3
2
1
0
0
5
10
15
20
viscosity (mPas)
25
30
MAIN CONCLUSIONS AND OUTLOOKS

Noteworthy differences in bacterial physiology at
increased viscosity / changed rheology:


variability in bacterial response
Changes in viscosity / rheology can affect:
growth rates
 total metabolic activity
 efficiency
 carbon flow through central metabolic pathways


Other bacteria might also be subject to changes
in environmental viscosity/rheology – can this
be the case in water treatment plants and
other biotechnological settings?
ACKNOWLEDGEMENTS

co-workers at the Chair of Microbiology,
Biotechnical Faculty, Ljubljana
prof. dr. David Stopar
 dr. Tjaša Danevčič


JUB, d.d.

Slovenian Research Agency